In recent years, there has been proposed a display apparatus that uses a plurality of display elements such as DMD (Digital Micromirror Device). The display apparatus, that uses the plurality of display elements, includes an optical synthesis optical system that is configured in which a plurality of projection lights emitted from the respective display elements are synthesized on the same optical axis, and projects the synthesized projection light. For example, Patent Literature 1 discloses a display apparatus that includes three DMDs as display elements, and a cross dichroic prism (hereinafter, referred to as XDP) as an optical synthesis optical system.
FIG. 1 is a diagram illustrating the configuration of the display apparatus described in Patent Literature 1. Display apparatus 1000 illustrated in FIG. 1 includes illumination optical system 100, light separation XDP 210, dichroic mirror 220, reflection mirrors 230 and 240, condenser lenses 250 and 260, three DMDs 300R, 300G, and 300B, three TIR (Total Internal Reflection) prisms 400R, 400G, and 400B, optical synthesis XDP 500, and projection lens 600.
A light exited from illumination optical system 100 is separated into a red light and the mixed light of green and blue at light separation XDP 210. The red light enters TI prism 400R via reflection mirror 240 and condenser lens 260. The mixed light of green and blue enters dichroic mirror 220 via reflection mirror 230 and condenser lens 250. At dichroic mirror 220, the mixed light of green and blue is separated into a green light and a blue light. The green light enters TIR prism 400G, and the blue light enters TIR prism 400B.
The lights respectively made incident on TIR prisms 400R, 400G, and 400B are totally reflected respectively on first surfaces 402R, 402G, and 402B, and respectively enter DMDs 300R, 300G, and 300B that each correspond to TIR prisms 400R, 400G, and 400B.
Each of DMDs 300R, 300G and 300B has a plurality of micromirrors arranged in a matrix in the image forming region and, by rotating each micromirror to change the reflection direction of light, modulates the incident light to emit the modulated light as image light. The image lights respectively emitted from DMDs 300R, 300G, and 300B are transmitted through TIR prisms 400R, 400G, and 400B that each correspond to DMDs 300R, 300G, and 300B to enter XDP 500.
XDP 500 has second surfaces 506 and 508 for transmitting or reflecting the incident image lights of respective colors, and emits a plurality of image lights incident on second surfaces 506 and 508 in the same direction to synthesize the image lights of respective colors. The synthesized image light is emitted from XDP 500 toward projection lens 600, and is then projected to a screen (not illustrated) via projection lens 600.
In XDP 500, S-polarized light or P-polarized light is reflected by second surfaces 506 and 508 while the other is transmitted through second surfaces 506 and 508. Thus, in order to efficiently synthesize the lights respectively emitted from DMDs 300R, 300G and 300B, the lights incident on second surfaces 506 and 508 are converted into S-polarized lights or P-polarized lights.
Further, DMDs 300R, 300G, and 300B are arranged such that the long side of the image forming region may be inclined by 45° to the side of the light incident surface of XDP 500. Therefore, display apparatus 1000 must be inclined by 45° from a horizontal direction to normally display a projected image.